Long-distance cable installation



Dec.9, 1930. K. FISCHER LONG DISTANCE CABLE INSTALLATION Filed March 51, 1928 2 Sheets-Sheet l Dec. 9, 1930. K. FISCHER LONG DISTANCE CABLE INSTALLATION Filed March 31, 1928 2 Sheets-Sheet 2 illiiiiill.

K, G {saher 19 points is kept the same.

20 is well known, limited attained according by this that for long Patented Dec. 9, 1930 UNITED STATES PATENT OFF! KUNO rxscnnn, or NUREMIBERG, GERMANY, Assienon T ST'JDDEUTSCHE TELE-F-ON- APPARATE-KABEL- UND DRAHTWERKE A,-G., 0F NUREMBERG, GERMANY LONG-DISTANCE CABLE INSTALLATION Application filed has a1, 1928, Serial No.

tween the amplifiers and the increase in the limit or critical frequency of the cable.

If the distance between the amplifiers is increased, the range of the total length is in creased although the number of amplification If the limit frequency is increased .whilst the distance between the amplifiers and the specific damping remain the same, the number of amplification points can be increased without any technical difliculties being encountered. In both cases it is thus possible to-increase the range of long lines.

The number of two-way amplifiers which can be inserted in a double line is, however, as by the requirement of an artificial line at each amplifying point, which artificial line can be reproduced exactly only to a limited extent, owing to the fluctuations in the attenuation of the line with respect to the telephone frequency. However,

if the limit frequency is increased, the fluctuations in the attenuation are reduced, whereby a better balance or reproduction of the artificial line can 'be obtained.

F or a given length of-telephone line, the

increase in range is naturally equivalent to a reduction in the cost to be incurred for the long distance installation. This results from the fact that, according to the present invention, a reduction in the damping of the line in order to increase the range is obtained without increasing the cross-section of wire, as has hitherto been necessary.

As' regards the two problems above mentioned, further substantial progress can be to the present invention distance cable installations with an inductive load of the cable and having side and phantom circuits and being provided with amplifiers, use is made of such cables in which each two single wires are twisted together into a pair of wires, of which four such pairs of wires into an eight-wire core, after be referred to as a the which will hereindouble star. In

' the range of are twisted together 266,248, and in Germany February 2, 1928 the double star, the side circuits areformed by the single'pairs of wires and the phantom circuits by each two diagonally opposite pairs of wires. Y

The cable combination just referred to is known per se. However, the importance of the method of twisting the wires of the cable into double stars and the formation of phantom circuits from such double stars in connection with the two problems above referred to has not hitherto been known and therefore the arrangement has not been either used or proposed. The arrangement, however, permits the ratio of the phantom capacity to the capacity of the side circuits to be reduced to 1.2, whereby the advantage is obtained that the telephone installation is increased.

According to the invention, instead of usingacable such as above referred to, other cables may be used, provided they ensure that the capacity ratio above mentioned is less than 1-2.

The invention is illustrated by way of exdrawings, in which Figure 1 is a cross-section of a cable used in connection with the present invention,

Figure 2 shows the electrical connections of the wires of a double star, and Figures 3, 4 and 5 illustrate different methods of carrying out a telephone cable installation according to the invention.

A cable according to Figure 1 comprises, for instance, twelve double stars. Each one of these double stars contains four pairs of wires a, b, c and'd, which are stranded together to a double star, each pair consisting of two single wires which are twisted together. The four pairs of wires of each double star constitute four side circuits, which are shown in Figure 2 and which are connected with telephone apparatus T F. The pairs of wires a and I}, which are shown in igure 1 to bediagonally opposite to one another on the one hand, and the pairs of wires 0 and d on the other hand are connected together to phantom circuits. These two phantom circuits of each double star are connected toother telephone apparatus T P over coils 6. By this method of stranding and electrical connections, the capacity of the phantom circuits in telephone cables is so reduced that the ratio of the said capacity to the capacity of the side circuits is reduced to a value less than 1-2.

In this way the advantages above referred to are attained, since the great reduction in the phantom capacity allows approximately double the limit frequency to be imparted to the phantom circuits, whilst the damping is the same as in the case of the side circuits, or to impart to them half the specific damping when the limit frequency is approximately the same as in the case of the side circuits.

In both cases the range of the telephone installation is increased. In the first case, it is even possible to use phantom lines which are not pupinized whereby the lines can have an unlimited high limit frequency so that it is possible to obtain an ideal balance. It is true that the damping and the distortion would be substantially increased. However, the damping of and the distortion in the lines can be entirely removed since the same amplifiers which were previously used are now fully utilized, which was not hitherto possible.

The various modes of carrying the invention into effect will now be described and reference will also be made to the formulae, which hold good for installations provided with amplifiers and with pupin coils. It will be assumed that the phantom capacity C is equal or approximately equal to the capacity Cf of the side circuits. The following formulae hold good In these formulae s=the distance between the coils of the installation in km. L=the inductance of the installation per km. C=the capacity of the installation per km. R=the resistance of the installation per km.

lVhen the formula (1) is used, it has to be borne in mind that the ohmic resistance R of the phantom circuits is half the value of the ohmic resistance of the side circuits. It then follows from the formula (1) that in the phantom circuits for the same damping b the limit frequency 1) according to formula (2) can be increased to the double value by reducing L.

On the other hand, half the damping may be imparted to the phantom circuits accord ing to the formula (1) for the same inductance L and the same damping b.

As stated above, in both cases the range of the telephone installation is increased.

Figure 3 shows a long distance cable installation in which the coil loading is such that the phantom circuits have half the specific damping of the side circuits when the limit frequency is approximately the same in the phantom and in the side circuits and consequently the distance between the amplifier points is doubled. Only two opposite pairs of wires a and b of a double star are shown, as this is sufficient for illustrating the construction of the installation. F S are the loading coils of the side circuits and P F the loading coils of the phantom circuits. F A and P A are the thermionic amplifiers which are inserted in the side and phantom circuits respectively. The distance between the amplifying points of the phantom lines is double the distance between the amplifying points of the side circuits.

Figure 4: shows along distance cable installation in which the loading coils are provided only for the side circuits and not also for the phantom circuits.

The distance between the amplifying points of the phantom circuits is the same as that between those in the side circuits.

When in an installation according to the present invention the inductive loading of the cable is uniform the self-inductances which lie in the side and phantom circuits are already determined by the iron wire winding which is provided around the individual conductors. However, irrespective of the self-inductances of the individual conductors, when such cables are used according to the present invention the damping of the phantom circuits is even less than that of the side circuits and the ratio of the damping of the phantom circuits to that of the side circuits is only about 0.7.

Figure 5 illustrates a long distance'cable installation similar to that illustrated in Figure 3 with that difference that the loading by means of pupin coils has been replaced by a uniform inductive loading according to Krarup. This form of loading has been indicated in connection with each individual conductor by an iron wire which is wound round the conductor along its whole length.

What I claim is:

1. Long distance cable installation comprising an inductively loaded cable and amplifiers along the cable,'in which each two individual conductors are twisted together to a pair of conductors and each four such pairs of conductors are twisted together to a double star and in which side circuits are formed of the individual pairs of conductors and phantom circuits are formed of each two diagonally opposite pairs so that the ratio of the capacity of the phantom circuits to the capacity of the side circuits is less than 1.2.

2. Long distance cable installation as claimed in claim 1 and in which the inductive loading consists of inductance coils lying in the side and in the phantom circuits, the

tributed only over the side circuits, the phanvalues of the inductance and of the resistance being such that the phantom circuits have, according to the formulae v the same damping as the side circuits and approximately double the limit frequency of the latter;

3. Long distance cable installation as claimed in claim 1, in which the inductive loading consists of inductance coils distom circuits having no inductive loading.

' 4. A long distance cable installation as claimed in claim 1 and in which the inductive loading consists of inductance coils distributed over the side and phantom circuits and in which the values of the inductance and resistance are such that the phantom circuits have, according to the formulae half the damping of the side circuits, while the limit frequenc of the phantom circuits is approximately t e same as that of the side circuits.

5. Long distance installation as claimed in claim 1 and in which the inductive loading consists of uniformly distributed inductances in the side and phantom circuits and in which the ratio of the damping of the phantom circuits to the damping of the side circuits is about 0.7.

In testimony whereof I have signed my name to this specification.

, KUNO FISCHER. 

